Visual acuity,sensitivity and binocularity in a gleaning insectivorous bat,Macrotus californicus (Chiroptera: Phyllostomidae)

Behavioural tests were used to examine the visual acuity and sensitivity of Macrotus californicus, a 12–14-g desert bat known to use vision in the location of terrestrial prey. Optomotor responses indicate single point visual acuity as fine as 3′38″ of arc. For comparison, the same tests were applied to two other species of bats. Antrozous pallidus, a desert gleaner which locates prey by the sounds they produce, exhibited acuity of 15′ of arc, and Eptesicus fuscus, an aerial foraging species that uses echolocation to find prey, 60′ of arc. Both M. californicus and A. pallidus retained their acuity at light levels as low as 2×10⁻⁴ mL (approximately 2×10⁻³ lux), comparable to ground luminance on a clear, moonless night. The eyes of M. californicus were more anteriorly directed, and had twice the binocular overlap of the other species examined. Comparison of our data with results from other studies indicate that M. californicus has vision superior to other insectivorous bats, and at least equivalent to larger-eyed frugivorous and nectarivorous bats examined in previous studies.